<!DOCTYPE html>
<html>
    <head>
        <script src="vue.js"></script>

    </head>
    <body>
        <div id="app">
            <!--input中的v-model用于在表单控件元素上创建双向数据绑定-->
            <input type="text" v-model="cityName">
        </div>
        <script>
            var vm = new Vue({
                el:'#app',
                data: {
                    cityName: 'shanghai'
                },
                //使用watch监听cityName变化
                watch: {
                    cityName (newName, oldName) {
                        console.log(newName, oldName)
                    }
                }
            })
        </script>
    </body>
</html>